I nearly missed a flight because of this foolishness. Back in 2009 I had renewed once and went back to Invercargill for the summer vacation. Coming back to Korea I got held up for 20 minutes at check in because I had no proof that I was actually allowed into the country, beyond an expired visa in my passport and a scribble on the back of my ARC (which means nothing to Air NZ).
I would have been kicked off the flight if I hadn't have persevered. Even the Korean rep for KAL said I wasn't legit. After a ton of ringing around (at my behest), they finally let me on the flight.
Korean immigration are totally unsympathetic to this as well. I asked them to issue me a brand new ARC with a legit date on it (at my expense), not just a scribble on the back and the guy wouldn't do it. He finally did after I persisted and some shouting (from him). It's a ridiculous situation, but last time I went home (on the same VISA as '09) I had no problems. So, in my experience, you have a 50/50 chance of being fine. Of course my problem could have been an isolated incident.